1. Field of the Invention
This invention relates generally to the field of angioplasty, the balloon-catheter reconstruction of a blood vessel. In particular, it relates to a unique passive perfusion balloon catheter for use in percutaneous transluminal angioplasty, which allows blood to flow through the artery between the arterial wall and the irregular surface of the balloon to the distal side of the stenosis during dilation of the blood vessel.
2. Description of the Related Art
Atherosclerosis is a debilitating disease that is characterized by irregularly distributed lipid deposits, called plaque, on and within the walls of arteries. Ultimately, atherosclerosis results in a narrowing of, and a total or partial occlusion of blood flow through, the arterial lumen. Atherosclerosis typically begins in the second or third decade of life and usually affects arteries throughout the vascular system in varying degrees.
In some portions of an affected artery, the build up of plaque results in a more severe narrowing called a "stenosis." If the stenosis is severe, blood flow is restricted or precluded and surgical or balloon catheter treatment is often necessary on clinical grounds to restore patency to the area. When stenosis is found over 70-80 % of a coronary artery, myocardial ischemia (the inadequate flow of oxygen rich blood to the myocardium, the muscle layer of the heart) can occur. Myocardial ischemia is sometimes accompanied by angina pectoris, a constricting pain in the chest, shoulder or arms. Also attendant with the progression of atherosclerosis are coronary artery spasm and the formation of life-threatening intraluminal thrombi, commonly referred to as blood clots.
Percutaneous transluminal angioplasty, using a balloon catheter, was first introduced in the mid-1970's and has become a widely accepted method for treating obstructed arteries. There are currently four basic designs employed in percutaneous transluminal angioplasty 1) standard balloon over a wire; 2) low profile, small shaft balloon over a wire; 3) standard shaft balloons with fixed or partially movable wires and 4) balloon on a wire system. The procedure will be described applying the first design.
The procedure is typically performed by first making a puncture wound in the patient's right groin to gain access to the right femoral artery. A guide wire is passed through the artery and advanced through the arterial system until the distal end of the wire reaches the arterial stenosis, whether iliac, femoropopliteal, aortic, renal, splanchnic, or brachiocephalic. For many stenosis, in particular those in coronary arteries, a guiding catheter is advanced over the guide wire until its distal end passes over the distal end of the guide wire. The guide wire is then removed and a special PTA (percutaneous transluminal angioplasty) wire is advanced through the guiding catheter up to the locus of the stenotic lesion. The physician then manipulates the proximal end of the PTA wire to pass it through the stenotic lesion that is obstructing the artery. Once the PTA wire passes successfully through the stenotic lesion, a PTA balloon angioplasty catheter is passed over the PTA wire by feeding the distal end of the balloon catheter over the proximal end of the wire and then pushing the balloon catheter over the wire until the balloon is adjacent to (within) the stenotic lesion. Thus positioned, the balloon is inflated by injecting thereinto a bio-compatible fluid, such as saline. As the balloon inflates, it stretches the artery wall, distorts the plaque defining (or forming) the stenotic lesion and frequently produces a tear in the inner layers of the vessel wall. The plaque is displaced thus improving or restoring patency to the target artery.
Conventional angioplasty catheters have the undesirable effect of completely denuding the intimal surface, the innermost layer of endothelial cells lining the artery, when the balloon surface contacts the intima. An intact endothelial surface prevents contact between platelets and other components of the intima which act as powerful agonists of platelet adhesion and activation. If the depth of arterial injury is extensive, a powerful stimulation of the clotting system may occur leading to thrombosis and occlusion. Limiting the extensive the loss of endothelial cells may protect against thrombosis. Thrombi which form in the arterial lumen can block blood flow despite a physician's successful efforts in displacing the plaque. One method of treating this problem has been the use of prolonged inflation periods. However, longer inflation times are only practical (can only be utilized) if the catheter allows blood to continue to flow through the artery.
Conventional angioplasty catheters used to perform percutaneous transluminal angioplasty also have the disadvantage of completely occluding blood flow while the balloon is expanded in the artery. This can cause damage to the arterial wall by preventing the endothelial and smooth muscle cells from absorbing oxygen and, if the stenosis is in a coronary artery, may cause serious damage to those portions of the heart that receive blood via that artery. Consequently, angioplasty is not only a painstaking task for the physician who must inflate the balloon for only a few seconds and then deflate the balloon to allow blood to continue to flow through the artery, but is also potentially dangerous for the patient. Indeed, if the balloon is inflated for longer than 60-90 seconds, the patient may experience severe angina, shock, and/or rhythm disturbances of the heart.
Angioplasty procedures currently being used in practice also result in a re-stenosis rate of 20-50%.
Attempts to overcome these problems have been met with limited success. For example, a passive perfusion-type balloon catheter has been developed which has blood entry side hole(s) proximal to the balloon and blood exit hole(s) distal to the balloon. The side holes permit blood to pass through the lumen of the catheter, by-passing the balloon and stenosis as the inflated balloon blocks the arterial lumen. However, typically such catheters have a large profile, even with the balloon deflated, because the main body of the catheter must be relatively large to allow the blood to flow therethrough, and are relatively stiff. These characteristics limit their usefulness as the primary catheter for very tightly stenosed arteries, small vessels or tortuous coronary arteries. Furthermore, although blood may flow straight through to the distal end of the stenosed region, the inflated balloon still occludes side branches and, therefore, does not protect the myocardium served by such side branching arteries from ischemia.
Additionally, the intimal surface which comes in contact with the inflated balloon is still completely denuded, making the subsequent formation of thrombi or restenosis more likely. Even further, since flow rates are proportional to arterial pressure in any passive perfusion system, patients with hypotension may not obtain relief of myocardial ischemia with the limited passive autoperfusion that conventional catheters allow.